'commit'

TangDou/AcWing/LCA/1172_BruteForce.cpp

@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+using namespace std;
+const int N = 40010, M = 80010;
+int e[M], h[N], idx, ne[M];
+void add(int a, int b) {
+    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
+}
+// 暴力法可以过掉 6/10
+int n;
+int depth[N];
+int fa[N];
+
+void bfs(int root) {
+    queue<int> q;
+    q.push(root);
+    depth[root] = 1;
+    fa[root] = -1;
+
+    while (q.size()) {
+        int u = q.front();
+        q.pop();
+        for (int i = h[u]; ~i; i = ne[i]) {
+            int v = e[i];
+            if (!depth[v]) {
+                depth[v] = depth[u] + 1;
+                fa[v] = u;
+                q.push(v);
+            }
+        }
+    }
+}
+
+int lca(int a, int b) {
+    if (depth[a] < depth[b]) swap(a, b);
+    while (depth[a] < depth[b]) b = fa[b];
+    while (a != b) a = fa[a], b = fa[b];
+    return a;
+}
+
+int main() {
+#ifndef ONLINE_JUDGE
+    freopen("1172.in", "r", stdin);
+#endif
+    memset(h, -1, sizeof h);
+
+    scanf("%d", &n);
+    int a, b, m, root;
+
+    for (int i = 0; i < n; i++) {
+        scanf("%d %d", &a, &b);
+        if (b == -1)
+            root = a;
+        else
+            add(a, b), add(b, a);
+    }
+    bfs(root);
+
+    scanf("%d", &m);
+    while (m--) {
+        scanf("%d %d", &a, &b);
+        int p = lca(a, b);
+        if (p == a)
+            puts("1");
+        else if (p == b)
+            puts("2");
+        else
+            puts("0");
+    }
+    return 0;
+}